1. Field of the Invention
The present invention relates to an expansion flexible tube joint and an assembling method thereof, and more particularly, to an expansion flexible tube joint which can be handled easily and is used for connecting water pipes, and because of its expanding flexibility, even when excessive external force is applied, the external force can be absorbed to prevent the tubes from being destroyed, and to an assembling method thereof.
2. Description of the Related Art
To already-existing tubes such as long water pipes provided on the ground or underground, various external forces such as compressing force, pulling force in the axial direction of the tube, or shearing force and bending moment in a direction perpendicular to the axial direction are applied due to ground subsidence or earthquake. If the external force is great, stress is concentrated on a tube joint which connects the already-existing tubes and the tube joint portion is destroyed. Therefore, it is necessary to absorb the external force applying to the water pipe portion to prevent the tube joint from being damaged.
Conventionally, a tube joint having a structure in which the tube joint itself can expand and contract is developed so as to absorb the external force to prevent the destruction. However, since this tube joint only move to expand and contract, the movable range is of two-dimensional, and this structure is not sufficient to cope with external force due to ground subsidence or earthquake.
To solve such a problem, there is developed a tube joint having a three-dimensional flexibility by employing a structure in which spherical surfaces are brought into contact with each other for sliding. In this case, as shown in FIG. 10, this expansion flexible tube joint A comprises a first cylindrical body 1, a second cylindrical body 2 and a third cylindrical body 3, and is connected to body tubes B at opposite flanges 6 through bolts 10 and nuts 11. The first cylindrical body 1 comprises a pair of spherical surface ring members 1, 1 made of cast iron and formed with partially spherical outer peripheral surface 4. The second cylindrical body 2 comprises a sleeve 2 made of cast iron and inserted into the first cylindrical body 1 for relative movement from an axis direction of the cylindrical body. The third cylindrical body 3 comprises a pair of casing tubes 3, 3 made of cast iron. The third cylindrical body 3 has an inner peripheral surface 5 for fitting over each of outer peripheral surfaces 4 of the first cylindrical body 1, and is formed at its opposite ends with flanges which are connecting portions. Because the expansion flexible tube joint A is formed in this manner, the sleeve 2, the spherical surface ring materials 1, 1 and two casing tubes 3, 3 are connected to one another such that they can extend and contract and move relative to one another. An end portion 3a of each of the casing tubes 3 is covered with a protective rubber cover 7, thereby preventing earth, sand, dust and the like from entering into sliding portions.
Further, an annular peripheral groove 1a is formed in an inner peripheral surface of the spherical surface ring material 1. An inner side of the annular peripheral groove 1a abuts against a C-shaped stainless steel lock-ring 17 having an angled cross section which is fitted and fixed to a recess formed in an outer peripheral surface of the sleeve 2 in the vicinity of its end. By this abutment, the relative movement range of the spherical surface ring material 1 and the sleeve 2 in the axial direction is limited. In FIG. 10, reference numbers 8 and 9 represent rubber seal rings.
In the case of this tube joint, when the outer peripheral surface 4 of the spherical surface ring material 1 swings while sliding on the inner peripheral surface of the casing tube 3, the outer peripheral surface of the sleeve 2 contact the end portion 3a of the casing tube 3 so that the swinging range is determined, but this range is set to a constant small angle range. That is, the inner peripheral surface of the end portion 3a of the casing tube 3 is chamfered off, and its angle is constantly set to 15.degree. and therefore, the swinging range of the tube joint is limited to the constant value.
However, in order to cope with megaseism or change with time of ground subsidence, development of small expansion flexible tube joint having excellent extending and retracting flexibility and capable of strongly exhibiting its function even if great external force is applied is highly required.